MPI_T_pvar_get_index(3)

💖 MPI_T_pvar_get_index(3) — the "bestie where is that variable" page 💖

okay so real talk: this is a page from the MPI manual (that's the Message Passing Interface, the whole parallel-computing thing, iykyk) and it's all about snagging the index of a performance variable. Like, you know the name of the pvar but you need the number? That's the whole gig. Slay. Let's go. 🦋

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✨ NAME ✨

MPI_T_pvar_get_index — get the index of a performance variable 👑

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🌸 SYNOPSIS 🌸

int MPI_T_pvar_get_index(const char *name, int var_class, int *pvar_index)

periodt, that's literally the whole signature, take it in bestie 💅

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🎀 INPUT PARAMETERS 🎀

• name — the name of the performance variable, and yes it's a string (a const char *, so pls don't go editing it, it's not yours to touch 🫶)
• var_class — the class of the performance variable, and this one's an integer

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⭐ OUTPUT PARAMETERS ⭐

• pvar_index — the index of the performance variable. it's an integer. that's THE drop. the index you came here for. 🎁

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🧚 THREAD AND INTERRUPT SAFETY 🧚

Good news first: this routine is thread-safe 💚 which means multiple threads can vibe with it at the same time and you don't have to bring your own thread locks. no user-provided locking, none, zero, we love to see it.

BUT — and this is the plot twist — it's not interrupt safe 😭 typically that's because it uses memory allocation routines like malloc, or other non-MPICH runtime routines that themselves aren't interrupt-safe. so like... respect the vibes, don't interrupt it mid-malloc. 💀

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🔥 ERRORS 🔥

okay so here's the whole error-handling situation, and it's A Lot, so buckle up bestie:

EVERY MPI routine (except MPI_Wtime and MPI_Wtick, those two are the exceptions, don't forget them) returns an error value. In C it comes back as the value of the function, and in Fortran it lands in the last argument. Before that value gets returned, the current MPI error handler gets called. By default, that error handler aborts the MPI job — yes, the whole thing, dramatic much?? 😭

You can change the error handler:

• MPI_Comm_set_errhandler for communicators
• MPI_File_set_errhandler for files
• MPI_Win_set_errhandler for RMA windows

There's also the MPI-1 routine MPI_Errhandler_set, but the manual says its use is deprecated — so like, we don't do that anymore, it's giving 2019. 🙈

And if you want errors returned to you instead of everything blowing up, the predefined error handler MPI_ERRORS_RETURN will do that for you. 💫

Real talk: MPI does not guarantee that an MPI program can continue past an error. That said, MPI implementations will attempt to continue whenever possible. So like... fingers crossed? 🤞

Here's the error code menu, no cap:

• MPI_SUCCESS — no error; the MPI routine completed successfully 🎉
• MPI_T_ERR_INVALID — invalid use of the interface or bad parameter values(s). yeah the typo "values(s)" is in the original, we keep it, we don't touch the sacred texts 💀
• MPI_T_ERR_INVALID_NAME — the variable or category name is invalid 🚫
• MPI_T_ERR_NOT_INITIALIZED — the MPI tool information interface is not initialized. you forgot to init it bestie, it happens to the best of us 😭
• MPI_ERR_OTHER — other error; use MPI_Error_string to get more information about this error code 🔍

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🌈 SEE ALSO 🌈

literally nothing listed here, so instead have a hug 🫶 and go read the rest of the MPI_T pages, they're all in the same era.

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okay that's the whole page, mwah, you ate it, go get that pvar index queen 👑 ✨

and for the sign-off: this was the MPI manual, MPI_T_pvar_get_index(3), dated 4/10/2026 — screenshot it, remember it, tell your friends. bye bestie 💖🎀🌸